1. Field of the Invention
This invention relates to a series of novel pyridazine analogs which exhibit selective inhibition of interleukin-1xcex2 converting enzyme, to compositions containing the novel pyridazine analogs and methods for therapeutic utility. More particularly, the interleukin-1xcex2 converting enzyme inhibitors described in this invention comprise novel pyridazine analogs which possess particular utility in the treatment of inflammatory, immune-based diseases and cancer.
2. Reported Developments
Interleukin-1xcex2 protease (also known as interleukin-1xcex2 converting enzyme or ICE) is the enzyme responsible for processing of the biologically inactive 31 kD precursor IL-1xcex2 to the biologically active 17 kD form (Kostura, M. J.; Tocci, M. J.; Limjuco, G.; Chin, J.; Cameron, P.; Hillman, A. G.; Chartrain, N. A.; Schmidt, J. A. Proc. Nat. Acad. Sci., 1989, 86, 5227-5231 and Black, R. A.; Kronheim, S. R.; Sleath, P. R. FEBS Let., 1989, 247, 386-391). In addition to acting as one of the body""s early responses to injury and infection, IL-1xcex2 has also been proposed to act as a mediator of a wide variety of diseases, including rheumatoid arthritis, osteoarthritis, inflammatory bowel disease, sepsis, and acute and chronic myelogenous leukemia (Dinarello, C. A.; Wolff, S. M., New Engl. J. Med., 1993, 328, 106). The naturally occurring IL-1xcex2 receptor antagonist has been used to demonstrate the intermediacy of IL-1xcex2 in a number of human diseases and animal models (Hannum, C. H.; Wilcox, C. J.; Arend, W. P.; Joslin G. G.; Dripps, D. J.; Heimdal, P. L.; Armes, L. G.; Sommer, A.; Eisenberg, S. P.; Thompson, R. C., Nature, 1990, 343, 336-340; Eisenberg, S. P.; Evans, R. J.; Arend, W. P.; Verderber, E.; Brewer, M. T.; Hannum, C. H.; Thompson, R. C., Nature 1990, 343, 341-346; Ohlsson, K.; Bjork, P.; Bergenfeldt, M.; Hageman, R.; Thompson, R. C., Nature, 1990, 348, 550-552; and Wakabayashi, G., FASEB, 1991, 338-343). The specific role of IL-1xcex2 in inflammation and immunomodulation is supported by the recent observation that the cowpox virus employs an inhibitor of ICE to suppress the inflammatory response of its host (Ray, C. A. et al, Cell, 1992, 69, 597-604).
The present invention also relates to the modulation of processing of IL-1xcex2 for the treatment of rheumatoid arthritis. Levels of IL-1xcex2 are known to be elevated in the synovial fluid of patients with the disease. Additionally, IL-1xcex2 stimulates the synthesis of enzymes believed to be involved in inflammation, such as collagenase and PLA2, and produces joint destruction which is very similar to rheumatoid arthritis following intraarticular injection in animals.
ICE is believed to be a cysteine protease (Thornbury, N.A. et al, Nature, 1992, 356-768). Peptidyl methyl ketone analogs constitute a wellknown class of compounds having cysteine protease inhibitory activity. (D. Rich in Chapter 4 of xe2x80x9cProteinase Inhibitorsxe2x80x9d, Barrett, A. J. and Salvensen, G., eds., Elsevier, 1986). However, there has never been a reported example of a non-peptide heterocyclic inhibitor of a cysteine protease. Hence, the inhibitory activity displayed by the pyridazine analogs described herein against ICE is unique.
An effective therapy has yet to be developed for the treatment of IL-1xcex2 mediated inflammatory diseases. Consequently, there is a need for therapeutic agents effective in the treatment and prevention of these diseases.
In accordance with the present invention, novel non-peptidic pyridazines are provided having the formula (I) and a pharmaceutically acceptable salt thereof 
wherein
R1 is a halogen, or an oxygen linked leaving group including an aromatic ether, an aromatic ester, an alkyl sulfonate, an aryl sulfonate, an alkyl phosphonate, an aryl phosphonate, an alkyl phosphate or aryl phosphate;
R2 is OR5, NH(CHR5)mxe2x80x94COOR5, NH(CHR5)mCON(R5)R6, N(R5)R6 or NH(CHR5)nOH;
R3 is H or alkyl;
R4 is H, substituted or unsubstituted aryl, heteroaryl or alkyl;
R5 and R6 are independently H, lower alkyl, aryl, heteroaryl, aralkyl, heteroaralkyl or lower cycloalkyl;
m=1-6; and
n=2-6.
As used herein, the term pharmaceutically acceptable salts includes the acid and base addition salts.
The term acid addition salts refers to those salts which retain the biological effectiveness and properties of the free bases and which are not biologically or otherwise undesirable, formed with inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid and the like, and organic acids such as acetic acid, propionic acid, glycolic acid, pyruvic acid, oxalic acid, maleic acid, malonic acid, succinic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, salicylic acid and the like.
The term base addition salts include those derived from inorganic bases such as sodium, potassium, lithium, ammonium, calcium, magnesium, iron, zinc, copper, manganese, aluminum salts and the like. Particularly preferred are the ammonium, potassium, sodium, calcium and magnesium salts derived from pharmaceutically acceptable organic non-toxic bases include salts of primary, secondary, and tertiary amines, substituted amines including naturally occurring substituted amines, cyclic amines and basic ion exchange resins, such as isopropylamine, trimethylamine, diethylamine, triethylamine, tripropylamine, ethanolamine, 2-dimethylaminoethanol, 2-diethylaminoethanol, trimethamine, dicyclohexylamine, lysine, arginine, histidine, caffeine, procaines, hydrabamine, choline, betaine, ethylenediamine, glucosamine, methylglucamine, theobromine, purines, piperazine, piperidine, N-ethylpiperidine, polyamine resins and the like. Particularly preferred organic non-toxic bases are isopropylamine, diethylamine, ethanolamine, trimethamine, dicyclohexylamine, choline and caffeine.
xe2x80x9cAlkylxe2x80x9d is defined as a saturated or unsaturated aliphatic hydrocarbon which may be either straight- or branched-chain. Preferred groups have no more than about 12 carbon atoms and may be methyl, ethyl and structural isomers of propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl and dodecyl.
xe2x80x9cLower alkylxe2x80x9d is defined as an alkyl group as above, having 1 to 4 carbon atoms. Suitable lower alkyl groups are methyl, ethyl, n-propyl, isopropyl, butyl, tert-butyl, n-pentyl, neopentyl, n-hexyl, and n-heptyl.
xe2x80x9cLower cycloalkylxe2x80x9d is defined as a carbocyclic ring of 3-8 carbon atoms including cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl.
xe2x80x9cArylxe2x80x9d is defined as phenyl, naphthyl and substituted phenyl.
xe2x80x9cSubstituted phenylxe2x80x9d is defined as a phenyl group in which one or more of the hydrogens has been replaced by the the same or different substituents including halo, lower alkyl, nitro, amino, acylamino, hydroxyl, lower alkoxy, aryl, heteroaryl, alkyl sulfonyl, arylfulsonamido, trifluoromethyl, morpholinoethoxy and morpholino-sulfonyl, and carbobenzoxy-methyl sulfamoyl.
xe2x80x9cHalogenxe2x80x9d is defined as chloride, fluoride, bromide or iodide.
xe2x80x9cHeteroarylxe2x80x9d is defined as pyridyl, thienyl, furyl, thiazolyl, imidazolyl, pyrazolyl, triazinyl, quinolyl and isoquinolyl.
xe2x80x9cSubstituted heteroarylxe2x80x9d means a heteroaryl group in which one or more of the hydrogens has been replaced by the the same or different substituents including halo, lower alkyl, nitro, amino, acylamino, hydroxyl, lower alkoxy, aryl, heteroaryl, lower alkoxy, alkylsulfonyl, trifluoromethyl, morpholinoethoxy, morpholino-sulfonyl, carbobenzoxy-methylsulfamoyl.
xe2x80x9cAralkylxe2x80x9d is defined as an alkyl group susbstituted by an aryl ring. For example, benzyl, phenethyl and 4-chlorobenzyl.
The present invention concerns a method for inhibiting ICE in a mammal by administering a therapeutically effective amount of a compound of the Formula (I) or a pharmaceutical composition containing a compound of the Formula (I) in a pharmaceutically acceptable carrier. The method of inhibition is directed for the treatment of IL-1xcex2 mediated disease states or disorders which include: infectious diseases, such as meningitis and salpingitis; septic shock, respiratory diseases; inflammatory conditions, such as arthritis, cholangitis, colitis, encephalitis, endocerolitis, hepatitis, pancreatitis and reperfusion injury, immune-based diseass, such as hypersensitivity; auto-immune diseases, such as multiple sclerosis; bone diseases; and certain tumors.
The pharmaceutical composition of the present invention comprises an active ingredient of the compound of formula (I) in admixture with a pharmaceutically acceptable, non-toxic carrier. Such compositions may be prepared for use for parenteral (subcutaneous, intraarticular, intramuscular or intravenous) administration, particularly in the form of liquid solutions or suspensions; for oral or buccal administration, particularly in the form of tablets or capsules; or intranasally, particularly in the form of powders, nasal drops or aerosols.
When administered orally (or rectally) the compounds will usually be formulated into a unit dosage form such as a tablet, capsule, suppository or cachet. Such formulations typically include a solid, semi-solid or liquid carrier or diluent. Exemplary diluents and vehicles are lactose, dextrose, sucrose, sorbitol, mannitol, starches, gum acacia, calcium phosphate, mineral oil, cocoa butter, oil of theobroma, alginates, tragacanth, gelatin, syrup, methylcellulose, polyoxyethylene sorbitan monolaurate, methyl hydroxybenzoate, propyl hydroxybenzoate, talc, and magnesium stearate.
The compositions may be prepared by any of the methods well-known in the pharmaceutical art, for example as described in Remington""s Pharmaceutical Sciences, 17th edition, Mack Publishing Company, Easton, Pa., 1985. Formulations for parenteral administration may contain as common excipients sterile water or saline, alkylene glycols such as propylene glycol, polyalkylene glycols such as polyethylene glycol, oils of vegetable origin, hydrogenated naphthalenes and the like. Examples of vehicles for parenteral administration include water, aqueous vehicles such as saline, Ringer""s solution, dextrose solution, and Hank""s solution and nonaqueous vehicles such as fixed oils (such as corn, cottonseed, peanut, and sesame), ethyl oleate, and isopropyl myristate. Sterile saline is a preferred vehicle and the compounds are sufficiently water soluble to be made up as a solution for all foreseeable needs. The vehicle may contain minor amounts of additives such as substances that enhance solubility, isotonicity, and chemical stability, e.g., antioxidants, buffers, and preservatives. For oral administration, the formula can be enhanced by the addition of bile salts and also by the addition acylcarnitines (Am. J. Physiol. 251:3332 (1986). Formulations for nasal administration may be solid and contain as excipients, for example, lactose or dextran, or may be aqueous or oily solutions for administration in the form of nasal drops or metered spray. For buccal administration typical excipients include sugars, calcium stearate, magnesium stearate, pregelatinated starch, and the like.
When formulated for nasal administration the absorption across the nasal mucous membrane is enhanced by surfactant acids, such as for example, glycocholic acid, cholic acid, taurocholic acid, ethocholic acid, desoxycholic acid, chenodesoxycholic acid, dehydrocholic acid, glycodeoxycholic acid, and the like (See, B. H. Vickery, xe2x80x9cLHRH and its Analogs-Contraception and Therapeutic Applicationsxe2x80x9d, Pt.2, B. H. Vickery and J. S. Nester, Eds., MTP Press, Lancaster, UK, 1987).
In general, for the uses as described in the present invention, it is expedient to administer the active ingredient in amounts between about 0.1 and 100 mg/kg body weight, most preferably from about 0.1 to 30 mg/kg body weight for human therapy, the active ingredient will be administered preferably in the range of from about 0.1 to about 20-50 mg/kg/day. This administration may be accomplished by a single administration, by distribution over several applications or by slow release in order to achieve the most effective results. When administered as a single dose, administration will most preferably be in the range of from about 0.1 to 10 mg/kg of body weight.
The exact dose and regimen for administration of these compounds and compositions will necessarily be dependent upon the needs of the individual subject being treated, the type of treatment, and the degree of affliction or need. In general, parenteral administration requires lower dosage than other methods of administration which are more dependent upon absorption.
Compounds of the present invention are prepared according to Schemes I, II and III. 
wherein
R2 and R3 are defined previously.
Referring to Scheme I, the condensation of a-keto esters with aryl ketones to provide 6-aryl-3-hydroxypyridazines has been previously described [Druey, J. and von Schmidt, P. (1954) Helv. Chim. Acta., Vol. 37, 134]. Diethyl ketomalonate (1) and the aryl ketone (2) are heated together neat to approximately 120xc2x0 C. for 15 hours to provide the condensation product (3). The keto-diester (3) is then treated with hydrazine in ethanol at reflux to form the 6-aryl-3-hydroxypyridazine (4), as crystalline solids. Saponification with aqueous alkali followed by neutralization provides the 3-hydroxy-carboxy-6-aryl-pyridazines (5). The conversion of 3-hydroxy-4-carboxy-6-aryl-pyridazines to their dichlorides (6) has been previously described in U.S. Pat. No. 4,590,194 and is performed by heating the pyridazines (5) with a halogenating agent (phosphorus oxychloride being the preferred agent) at reflux temperature (80xc2x0 C.) for 4 hours. The halogenating agent may be used neat or with inert solvent such as dioxane or toluene. The addition of a catalytic amount of DMF accelerates the reaction. Other suitable halogenating agents include phenylphosphinic dichloride and phorphorus trichloride.
The corresponding 3-bromopyridazines are prepared similarly by heating (5) with phosphorous oxybromide or phosphorus tribromide. The dichlorides (6) are isolated from the reaction mixture by removing excess halogenating agent and solvent in vacuo and dissolving the residue in hot acetonitrile or other polar inert solvent. The reaction of the dichlorides (6) in acetonitrile with alcohols or amines yield the desired esters or amides (7).
Referring to Scheme II, intermediate ketomalonate addition products (2) can be prepared by deprotonatoin of the acetophenones (1) with lithium diisopropylamine (LDA) followed by the addition of ketomatonate. This procedure was generally used for electron-rich aryl methyl ketones. 
wherein R is phenyl, substituted aryl or heteroaryl. 
Referring to Scheme III, the intermediate 3,5-difluoro-4-(methylsulfonyl)-acetophenone (6) was prepared from commercially available 2,6-difluoroaniline. Bromination of the aniline (1) in acetic acid followed by diazotization and treatment of the diazonium salt with dimethylsulfide provides the thiomethyl derivative (3). Palladium catalyzed coupling reaction of (3) with trimethylsilyacetylene yield arylacetylene (4).
Alkaline hydrolysis of the silyl group followed by mercuration and acidic solvolysis affords ketone (5). Oxidation of the ketone with Oxone provides the desired 3,5-difluoro-4-(methylsulfonyl)-acetophenone (6).